Value of type '<typename1>' cannot be converted to '<typename2>'


Updated: July 20, 2015

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Value of type '<typename1>' cannot be converted to '<typename2>'. Type mismatch could be due to the mixing of a file reference with a project reference to assembly '<assemblyname>'. Try replacing the file reference to '<filepath>' in project '<projectname1>' with a project reference to '<projectname2>'.

In a situation where a project makes both a project reference and a file reference, the compiler cannot guarantee that one type can be converted to another.

The following pseudo-code illustrates a situation that can generate this error.

' ================ Visual Basic project P1 ================

' P1 makes a PROJECT REFERENCE to project P2

' and a FILE REFERENCE to project P3.

Public commonObject As P3.commonClass

commonObject = P2.getCommonClass()

' ================ Visual Basic project P2 ================

' P2 makes a PROJECT REFERENCE to project P3

Public Function getCommonClass() As P3.commonClass

Return New P3.commonClass

End Function

' ================ Visual Basic project P3 ================

Public Class commonClass

End Class

Project P1 makes an indirect project reference through project P2 to project P3, and also a direct file reference to P3. The declaration of commonObject uses the file reference to P3, while the call to P2.getCommonClass uses the project reference to P3.

The problem in this situation is that the file reference specifies a file path and name for the output file of P3 (typically p3.dll), while the project references identify the source project (P3) by project name. Because of this, the compiler cannot guarantee that the type P3.commonClass comes from the same source code through the two different references.

This situation typically occurs when project references and file references are mixed. In the preceding illustration, the problem would not occur if P1 made a direct project reference to P3 instead of a file reference.

Error ID: BC30955

To correct this error

  • Change the file reference to a project reference.

Type Conversions in Visual Basic
Managing references in a project
NIB How to: Add or Remove References By Using the Add Reference Dialog Box